1. Field of the Invention
The present invention pertains to a method for detecting the presence of a color marker dye in aged or discolored diesel fuel and similar petroleum distillates.
2. Background
Petroleum distillate fuels such as regular, low-sulfur and crude diesel fuel and naval distillate fuel tend to discolor or darken, particularly with age. The formation of colored substances and darkening upon aging of these fuels masks the ability to visually detect the presence of certain marker dyes. This is particularly true if only a small amount of fuel has been dyed and then commingled with an undyed fuel.
The requirements to place visually detectable marker dyes in diesel fuels are carried out to mark or distinguish different grades of fuel and to distinguish fuels which are used for purposes which are subject to various taxes. For example, fuels sold for residential heating purposes and not subject to motor vehicle taxes are sometimes substituted for fuels which are normally subject to this tax to thereby avoid payment of the tax. Accordingly, there is a continuing and growing need to be able to detect the presence of marker dyes in diesel and similar distillate fuels to police improper use of these fuels and to meet regulatory requirements with respect to the use of different grades of fuel, particularly in motor vehicle applications.
Several inventions have been made using the concept of solid phase extraction to identify the presence of a marker dye in petroleum distillate fuels. My U.S. Pat. No. 4,918,020, issued Apr. 17, 1990, describes a solid phase extraction technique for isolating a particular commercially available marker dye in automotive gasoline. A bonded silica extraction column is provided and a sample of gasoline is passed through the column after preconditioning the column with a buffer solution. A commercially available reagent is then added to the column to form a colored complex with the marker dye which has been retained on the column.
Another solid phase extraction method is the subject of my U.S. patent application Ser. No. 07/920,071. filed Jul. 27, 1992 and assigned to the assignee of the present invention. The invention described in the above-referenced application is a method for determining the presence of DuPont Chemicals Oil Color IAR liquid marker dye in automotive gasoline by mixing a sample of the gasoline suspected of containing the dye with fine ground silica, particularly unbonded, flash chromatography grade silica to observe and compare the coloration of the silica and thereby detect the presence of the dye.
However, the use of unbonded silica as an extraction material for aged and colored petroleum distillates, such as diesel fuel, has not been contemplated heretofore since the coloring agents in such fuels are strongly polar and, it was believed, would tend to mask or prevent retention of a marker dye on the extractant material. Contrary to this belief and with the steps of the method of the present invention, it has been discovered that a visually detectable marker in colored diesel fuel can be detected even in small quantities using silica solid phase extraction columns. The advantages and a detailed description of this invention are set forth hereinbelow. A somewhat related discovery is the subject of my patent application entitled: "Detection of Marker Dyes in Aged or Dirty Motor Gasolines" filed of even date herewith.